The U.K. Supreme Court on Tuesday began hearing a legal challenge focusing on the definition of “woman” in a long-running dispute between a women’s rights campaign group and the Scottish government.

Five judges at Britain’s highest court were considering the case, which seeks to clarify whether a transgender person with a gender recognition certificate that recognizes them as female can be regarded as a woman under equality laws.

While the case centers on Scottish laws, the campaign group bringing the challenge, For Women Scotland (FWS), has said its outcomes could have U.K.-wide consequences for sex-based rights as well as everyday single-sex services such as toilets and hospital wards.